The present invention relates to extrusion dies and a method for making a cellular honeycomb structure, particularly, ceramic honeycomb structures for use as catalytic converters in the exhaust stream of internal combustion engines. While the invention may be used in other types of dies, it is especially suited for use in extrusion dies for manufacturing high cell density thin-walled honeycomb structures from an extrudable material, such as ceramic, and will be particularly described in that connection.
Dies having thin slot widths, that is, slot widths under 0.007 inches are difficult and costly to machine. As the slot width decreases, the tooling used for generating the slot needs to be reduced accordingly. Generally, the tooling blades are thin disc blades/cutters that are approximately two inches round in diameter. Reducing the thickness of the tooling blades tends to compromise the structural integrity of the tooling blades, making the blades somewhat weaker and a lot more difficult to control. Also, when the tooling blades are made thinner, the machining time is increased because the machining forces must be reduced to accommodate the reduced size of such thinner tooling blades. As a result, the quality of the die slots can be compromised. Alternatively, an electroplating process can be used to generate the die slots. In the electroplating process the material to be plated is carried in solution and a potential is used to move the material from the solution to the surface to be plated. If a large volume of solution is available at the surface of the part to be plated the plating material is readily replaced as it is deposited on the surface. When a die is plated, the solution must pass through the die to carry the plating material to the sides of the slots. As the passages become narrower, it becomes more difficult to move the solution through the die making it more difficult to adequately supply sufficient plating material along the entire passage. Also, as the surfaces being plated come closer together, the possibility of the plating material accumulating and bridging across the gap increases. This can prevent the material flowing through the die from forming a continuous web. In both approaches, there is no real indication of the success of the die until a product has been extruded and major expenses have been incurred.
Another problem with constructing thin slot dies is that the dimensions of the thin slots are determined by the dictates of the die design for the cellular product configuration. For example, if a die requires a slot depth of 0.100 inches, to insure good knitting of the extruded material, and to produce thin webs/walls in the product, this would mean that the thin slots would have to be cut to this depth of 0.100 inches. Since die slots are normally cut with a gang of disc blades/cutters assembled to the width of the product to be cut, at times there may be approximately 60 disc blades in an assembly. In such instances, trying to effectively cut a 0.003 inch slot width to a depth of 0.100 inches becomes very difficult, since some of the blades tend to shatter in the process.
In light of the foregoing, it is desirable to provide an extrusion die that can be used to form a cellular honeycomb structure with thin slots, and having a higher cell density. In addition, it is desirable to provide a device that incorporates an existing extrusion die in order to produce a quality cellular honeycomb structure with a higher cell density and thin walls. Furthermore, it is desirable to provide a more reliable method of making expensive extrusions dies for forming high cell density honeycomb structures with thin slots.
Accordingly, the present invention is directed to an extrusion die and a method of constructing an extrusion die that can be used to manufacture a surface area that substantially obviates one or surface area that substantially obviates one or more of the limitations and disadvantages of the related art. The principal advantage of the present invention is the provision of an arrangement that overcomes the limitations and disadvantages of the described prior arrangements. Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus particularly pointed out in the written description and claims hereof as well as the appended drawings.
The invention provides a method of capping a cellular extrusion die base element for extruding a cellular honeycomb structure having a plurality of cell walls, where each cell wall has a thickness not greater than 0.007 inches, preferably, a thickness that is approximately in the range of 0.002 inches to 0.007 inches, and most preferably, a thickness under 0.006 inches. The extrusion die base element is provided with a grid of separate feed holes/feed channels originating at an inlet face of the base element, and terminating at an outlet end within and proximate to an outlet face of the base element. Further, each of the feed channels are in direct communication with one of a matrix of intersecting pairs of primary outlet slots. In one embodiment, the base element further comprises another matrix of intersecting pairs of secondary outlet slots, where each one of the matrix of intersecting pairs of secondary outlet slots bisects each one of the matrix of intersecting pairs of primary outlet slots, and where the intersecting pairs of primary outlet slots and secondary outlet slots form a matrix of square shaped pins/pegs that terminate at the outlet face of the base element. The method further includes scoring a plurality of indentations or notches into that region of the outlet face of the base element that does not contain any of the intersecting pairs of primary outlet slots nor any of the secondary outlet slots. Alternatively, the scoring step includes scoring indentations or notches into a first side of the capping plate and scoring indentations or notches into that region of the outlet face of the base element that does not contain any of the intersecting pairs of primary outlet slots nor any of the secondary outlet slots. The method further includes filling a filler material into each of the feed channels. In an alternative embodiment, the method includes filling each of the feed channels and each of the primary outlet slots and secondary outlet slots with a filler material. The method further comprises placing a uniform layer of bonding material onto the outlet face of the base element and into each of the indentations and then permanently securing the first side of a capping plate to the outlet face of the base element to form a composite extrusion die. The method further comprises cutting a matrix of intersecting pairs of cap slots through the capping plate such that, at an inlet end of each of the cap slots, each of the cap slots is in direct communication with each of both the primary outlet slots and the secondary outlet slots and an opposite outlet end of each of the cap slots, terminates at an opposite outlet face of the composite extrusion die. Each of the cap slots are cut to have a slot width that is smaller than a slot width of each of the primary outlet slots and the secondary outlet slots, where the slot width of each of the cap slots is preferably not greater than 0.007 inches, preferably, a thickness approximately in the range of 0.002 inches to 0.007 inches, and most preferably, a thickness under 0.006 inches. Finally, the method comprises eliminating the filler material within each of the feed channels and within each of the primary outlet slots and the secondary outlet slots.
Additionally, the invention provides a method of making a composite cellular extrusion die for extruding a cellular honeycomb structure having cell walls with a thickness not greater than 0.007 inches, preferably, a thickness approximately in the range of 0.002 inches to 0.007 inches, and most preferably, a thickness under 0.006 inches. The method includes the steps of drilling a grid of separate feed holes/channels originating at an inlet face of an extrusion die base element and terminating at an outlet end that is within and proximate to an outlet face of the base element. The method further comprises cutting a grid of intersecting primary outlet slots into the outlet face of the base element, where every alternate one of the grid of intersecting primary outlet slots is in direct communication with the outlet end of a plurality of the feed channels. Furthermore, the method includes cutting a grid of intersecting secondary outlet slots 34 into the outlet face of the base element, where each one of the grid of intersecting secondary outlet slots bisect each one of the grid of intersecting primary outlet slots. The method further includes scoring a plurality of indentations into that region of the outlet face of the base element that does not contain any of the primary outlet slots and secondary outlet slots, and filling each of the feed channels and each of the primary outlet slots and secondary outlet slots with a filler material. In an alternative embodiment, the scoring step includes scoring a plurality of indentations into a first side of the capping plate and scoring a plurality of indentations into that region of the outlet face of the base element that does not contain any of the intersecting pairs of primary outlet slots nor any of the secondary outlet slots. Further, the method includes placing a bonding material onto the outlet face of the base element and into each of the plurality of indentations. Finally, the method includes permanently attaching, to the outlet face of the base element, a first side of a capping plate having a plate thickness not greater than 0.060 inches, preferably not greater than 0.025 inches, and cutting through the capping plate a grid of cap slots having a slot width not greater than 0.007 inches, preferably, a thickness approximately in the range of 0.002 inches to 0.007 inches, and most preferably, a thickness under 0.006 inches, such that, an inlet end of each of the cap slots is in direct communication with one of the grids of intersecting pairs of primary outlet slots and an outlet end of each of the cap slots terminates at an outlet face of the composite die, where each of the secondary outlet slots has a slot width that is at least equal to the slot width of each of the primary outlet slots, and where each of the secondary outlet slots has a slot depth that is less than a slot depth of each of the primary outlet slots. In a preferred embodiment, each of the secondary outlet slots has a slot width that is larger than the slot width of each of the primary outlet slots. The method further comprises eliminating the filler material from each of the feed channels and each of the primary outlet slots and secondary outlet slots. Furthermore, the method includes, prior to the attaching step, first extruding an extrudable material through the base element to test the performance of the base element in forming a test cellular honeycomb structure.
In yet another embodiment, the invention provides a method of making a cellular honeycomb structure having a plurality of cell walls with a thickness not greater than 0.007 inches, preferably, a thickness approximately in the range of 0.002 inches to 0.007 inches, and most preferably, a thickness under 0.006 inches. The method comprises the steps of providing the base element with a grid of separate feed channels originating at an inlet face of the base element and terminating at an outlet end within and proximate to an outlet face of the base element. The feed channels are in direct communication with one of a matrix of intersecting pairs of primary outlet slots, where each one of the matrix of intersecting pairs of primary outlet slots is in direct communication with each one of the matrix of intersecting pairs of secondary outlet slots. The method further comprises scoring a plurality of indentations into that region of the outlet face of the base element that does not contain any of the primary outlet slots and secondary outlet slots, and filling each of the feed channels and each of the primary outlet slots and secondary outlet slots of the base element with a filler material. The method further comprises placing a bonding material onto the outlet face of the base element and into each of the indentations, and permanently bonding a capping plate having a thickness not greater than 0.0025 inches to the outlet face of the base element to form a composite die structure. Additionally, the method comprises cutting a matrix of intersecting pairs of cap slots through the capping plate, such that an inlet end of each of the cap slots within the composite die structure is in direct communication with each of the primary outlet slots and an opposite outlet end of each of the cap slots, terminates at an opposite outlet face of the composite die structure. In one embodiment, each of the secondary outlet slots has a slot width that is at least equal to the slot width of each of the primary outlet slots, and each of the secondary outlet slots has a slot depth that is less than a slot depth of each of the primary outlet slots. In a preferred embodiment, each of the secondary outlet slots has a slot width that is larger than the slot width of each of the primary outlet slots. Further, each of the cap slots has a slot width that is smaller than a slot width of each of the primary outlet slots. Finally, the method includes the step of extruding an extrudable material out through the cap slots, where each of the cap slots has a slot width, preferably, not greater than 0.007 inches.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the extrusion die is for making a cellular ceramic honeycomb structure used in catalytic systems. Furthermore, a method is provided for making the extrusion die and for making the honeycomb structure using the extrusion die of the present invention.